Menses blood is a bit black what problem is

If a small amount of menstrual blood blackening is a normal phenomenon, it may be caused by the long time that menstrual blood is deposited in the vagina; but a large amount of menstrual blood blackening may be caused by palace cold, cervical erosion and pelvic inflammation, etc., and can go to the hospital for gynecological examination three days after menstruation is clean.